Double combustion oxygen enhanced sulfur recovery process

Abstract

A feed gas stream containing at least 60% by volume of hydrogen sulphide is burnt in a first combustion region to form water vapor and sulphur dioxide. Oxygen is employed to support combustion is the region. Thermal reaction then takes place in a thermal reaction region between hydrogen sulphide and sulphur dioxide to form sulphur vapor and water vapor. The resulting gas mixture is then cooled and sulphur vapor is extracted in a condenser. The gas mixture then passes into a second combustion region in which a further portion of the hydrogen sulphide is burnt in the presence of oxygen to form further sulphur dioxide and to adjust the mole ratio of hydrogen sulphide to sulphur dioxide to about 2:1. Further reaction between hydrogen sulphide and sulphur dioxide may be conducted in a further thermal reaction region and in catalytic reactors with further sulphur extraction in further condensers. The mole ratio of hydrogen sulphide to oxygen entering the first combustion region per unit time is greater than 2:1 and the mole ratio of hydrogen sulphide to fluid(s) (if any) other than oxygen being introduced into the first combustion region is greater than 3:2 and preferably greater than 4:1. By using substantially pure oxygen to support combustion of the hydrogen sulphide, a relatively large flow rate of feed gas mixture may be handled in a plant of given size.

I claim: 
     
       1. A method of recovering sulphur from a feed gas stream comprising at least 60% by volume of hydrogen sulphide, including burning less than 33 mole percent of the hydrogen sulphide content of the feed gas stream in a first combustion region to form water vapour and sulphur dioxide, introducing oxygen into the combustion region to support the combustion of the hydrogen sulphide, reacting unburnt hydrogen sulphide with said sulphur dioxide in the thermal reaction region associated with the first combustion region to form sulphur vapour and water vapour, the mole ratio of hydrogen sulphide to oxygen entering the combustion region per unit time being greater than 2:1, and the mole ratio of hydrogen sulphide to fluids, if any, other than oxygen being introduced into the combustion region per unit time being greater than 3:2, taking a resultant gas mixture comprising water vapour, sulphur dioxide, hydrogen sulphide, and sulphur vapour, from said thermal reaction region, extracting the sulphur vapour from the resultant mixture, reacting in at least one catalytic region hydrogen sulphide contained in the resulting gas mixture with sulphur dioxide contained in the resultant gas mixture to form further sulphur vapour and water vapour, and extracting said further sulphur vapour from the gas mixture, wherein the mole ratio of said hydrogen sulphide to sulphur dioxide is adjusted upstream of said at least one catalytic region by burning a further portion of the hydrogen sulphide content of the resulting gas mixture in a second combustion region to bring the mole ratio to the stoichiometric value or one approximating thereto, wherein there is never gas recycle to said first combustion region from downstream of said thermal reaction region. 
     
     
       2. A method as claimed in claim 1, in which said mole ratio of hydrogen sulphide to fluid, if any, other than oxygen being introduced into the combustion region per unit time is greater than 4:1. 
     
     
       3. A method as claimed in claim 1, in which the oxygen used to support combustion in the first combustion region is pure. 
     
     
       4. A method as claimed in claim 3, in which the only fluid other than hydrogen sulphide and oxygen introduced into the first combustion region is whatever fluid, if any, other than hydrogen sulphide is originally present in the feed gas mixture. 
     
     
       5. A method as claimed in claim 1, in which the proportion of the hydrogen sulphide in the feed gas mixture that is burnt in the first combustion region is chosen to give a flame temperature of at least 1300° C. in said first combustion region. 
     
     
       6. A method as claimed in claim 1, in which up to 25 mole per cent of the hydrogen sulphide content of the feed gas stream is burnt in the first combustion region. 
     
     
       7. A method as claimed in claim 1, in which the second combustion region is intermediate the location where sulphur vapour is extracted from said resultant gas mixture and said at least one catalytic region. 
     
     
       8. A method as claimed in claim 1, in which pure oxygen is used to support combustion in the second combustion region. 
     
     
       9. A method as claimed in claim 1, in which reaction takes place between hydrogen sulphide and sulphur dioxide in a second thermal reaction region downstream of the second combustion region to form water vapour and sulpur vapour, the gas mixture leaving the second thermal region is cooled, and its sulphur vapour is extracted. 
     
     
       10. A method as claimed in claim 9, in which the gas mixture leaving the second thermal reaction region is cooled to a temperature in the range of 300° C. to 400° C. and is then subjected to reaction over a catalyst whereby some of the residual hydrogen sulphide reacts with sulphur dioxide to form further sulphur vapour and water vapour, there being no means for extracting sulphur vapour intermediate said second thermal region and the catalyst. 
     
     
       11. A method as claimed in claim 9, in which all of the gas mixture leaving the location where sulphur vapour is extracted from said resultant mixture is subsequently passed through the second combustion region. 
     
     
       12. A method as claimed in claim 9, in which some of the gas mixture leaving the location where sulphur vapour is extracted from said resultant mixture by-passes the second combustion region. 
     
     
       13. A method as claimed in claim 12, in which the by-passed gas mixture is united upstream, in, or downstream of the second thermal reaction region with the gas that leaves the second combustion region. 
     
     
       14. A method as claimed in claim 1, in which the feed gas mixture contains at least 70% by volume of hydrogen sulphide. 
     
     
       15. A method as claimed in claim 1, in which there is a plurality of catalytic reaction regions. 
     
     
       16. Apparatus for recovering sulphur from a feed gas stream comprising hydrogen sulphide, comprising means for burning less than 33 mole percent of the hydrogen sulphide content of the feed gas stream in a first combustion region to form water vapour and sulphur dioxide; means for introducing oxygen into the combustion region to support the combustion of the hydrogen sulphide; a thermal reaction region, in association with the combustion region, for reacting unburnt hydrogen sulphide with said sulphur dioxide to form sulphur vapour and water vapour; first means for extracting the thus formed sulphur vapour; downstream of said extracting means at least one catalytic reaction region for reaction between hydrogen sulphide and sulphur dioxide to form further water vapour and sulphur vapour; second means for extracting said further sulphur vapour, and means for adjusting the mole ratio of said hydrogen sulphide to sulphur dioxide to bring it to the stoichiometric value or one approximating thereto, said adjusting means comprising a second combustion region upstream of said at least one catalytic region and additionally including a by-pass conduit having an inlet communicating with the outlet for gas of the first sulphur extraction means, and an outlet terminating downstream of the second combustion region and upstream of, in, or downstream of the second thermal reaction region, and wherein there is no means for recycling gas to said first combustion region from downstream of said thermal reaction region. 
     
     
       17. Apparatus as claimed in claim 16, wherein the thermal reaction region has heat exchange means associated therewith for reducing the temperature of the gas mixture upstream of the first sulphur extraction means. 
     
     
       18. Apparatus as claimed in claim 16, in which the second combustion region is intermediate the first sulphur extraction means and said at least one catalytic reaction region, and additionally including a second thermal reaction region associated with the second combustion region. 
     
     
       19. In a process for the production of sulfur by reaction of hydrogen sulfide and sulfur dioxide wherein a feed of hydrogen sulfide is oxidized in part to sulfur dioxide to form reactants which yield sulfur by the modified catalytic Claus reaction, the improvement which comprises: (a) introducing to a first combustion zone at least a portion of hydrogen sulfide rich gas stream containing at least about 10% by volume hydrogen sulfide and a first oxygen rich gas containing at least about 30% by volume oxygen in a proportion to achieve by combustion a first sulfur dioxide containing product gas stream at a combustion flame temperature of from about 1000° F. to about 3600° F.;   (b) cooling the first product gas stream to a temperature from about 240° F. to about 3000°; and   (c) introducing the cooled first product gas stream to at least a second combustion zone with additional oxygen rich gas stream containing at least about 30% by volume oxygen to combust additional hydrogen sulfide and yield a second sulfur dioxide containing product gas stream at a combustion flame temperature of from about 1000° F. to about 3600° F., the amount of hydrogen sulfide and oxygen fed to the combustion zones being proportioned to provide on completion of combustion a gas stream having a mole ratio of hydrogen sulfide to sulfur dioxide of about 2:1 for feed to a catalytic Claus convertor to achieve formation of sulfur by reaction of residual hydrogen sulfide with sulfur dioxide formed during combustion in the combustion zones.